(1) Field of the Invention
The present invention generally relates to a metal ion laser. More particularly, the present invention relates to an improvement in a configuration of a reservoir for storing metal material to be evaporated in the metal ion laser, and in a cooling system for cooling this laser in order to improve oscillating efficiency of laser light.
(2) Description of the Prior Art
In recent years various hollow-cathode type metal ion lasers, which use negative glow discharge, have been provided. Such type lasers are capable of multi-colors oscillation owing to their high intensive excitation. At the present stage we observe that a He-Cd ion laser can provide twelve light oscillating lines including three primary colors; i.e., red, blue and green. The He-Cd ion laser with this inherent property is superior to a liquid laser and a solid state laser.
Referring to FIG. 14, there is shown a typical example of such a hollow-cathode type metal ion laser as disclosed in Japanese Patent Application No. Sho. 58-236060. In this drawing, "a" represents a laser tube made of a glass material, which sealingly contains He gas. "b" and "c" represent Brewster windows sealingly secure to both ends of the laser tube "a". Further, the laser tube "a" contains a hollow-cathode "d", main anodes e.sub.1, e.sub.2 and e.sub.3, auxiliary anodes f.sub.1 and f.sub.2, an insulator "g", and flat-shaped reservoirs h.sub.1 and h.sub.2 formed between a laser tube "a" and hollow-cathode "d" for the metal material "i" to be evaporated. In a thusly constituted metal ion laser, a required predetermined voltage is applied between the main and auxiliary anodes e.sub.1, e.sub.2, e.sub.3, f.sub.1 and f.sub.2 and the hollow-cathode "d" so as to generate negative glow discharge between the main anodes and the hollow-cathode. If Cd is used as the metal material "i" to be evaporated, that is to provide a He-Cd type laser, Cd evaporates owing to the heat loss of the negative glow discharge. The evaporated Cd is excited to a high energy level by the excited particles of He ion, and then laser oscillation is generated.
On the other hand, such a hollow-cathode type metal ion laser involves a sputtering phenomenon caused by the cathode. Even if it is possible for the material for the cathode to be selected so as to decrease the sputtering, it is impossible to eliminate such sputtering completely. The sputtered product is discharged out of the cathode bore and moves towards the Brewster windows whose temperature is relatively lower than the cathode. Although the majority of the sputtered product is deposited on the parts, whose temperature is relatively low, in the laser tube before it arrives at the Brewster windows, the rest arrives at the Brewster windows and a considerable amount is deposited thereon. This deposited product makes the windows poor in their transparency. This causes a serious problem in that light loss at the Brewster windows becomes large, and thus the laser oscillation may become impossible. In addition to this problem, this deposition of the sputtered product shortens the length of life of the laser tube. On the other hand, the sputtered product exits out of the cathode bore at a relatively slow speed, so that the sputtered product moving slowly in the cathode bore may intercept the passage of light in the laser tube. This increases loss of the light of the laser oscillation, thereby worsening the efficiency of laser oscillation.
Further, the sputtered product may be deposited and pile-up in the vicinity of the anodes e.sub.1, e.sub.2 and e.sub.3, and on the metal materials "i" to be evaporated. This deposited product in the vicinity of the anodes may cause troubles, such as a short-circuit between the anodes and the hollow cathode. The piled up product on the metal materials may obstruct the evaporation of these metals and/or may be evaporated again. These phenomena may worsen the efficiency of the laser oscillation.
(3) Object of the Invention
With these problems in mind, it is an object of the present invention to provide an improved metal ion laser which can be free from the troubles owing to the product caused by sputtering.
Another object of the present invention is to provide an improved metal ion laser which can prevent the sputtered product from depositing on the vicinity of the anodes, metal material to be evaporated, and Brewster windows.